1. Technical Field
The present invention relates to a stereoscopic display for switching between a two-dimensional (2D) mode and a three-dimensional (3D) mode, and more particularly, to a stereoscopic display for generating a horizontal parallax or a vertical parallax using two polarization grating screens.
2. Related Art
A related art three-dimensional (3D) image is produced by combining two images separately captured by the left eye and the right eye. Because the human eyes are separated by about 65 mm from each other, the images of an object sensed by the respective eyes are slightly different. This difference is called binocular parallax and is the most important factor in producing a 3-D effect. Recent related art demands for stereoscopic displays that provide a stereoscopic image using binocular parallax have greatly increased in various fields, such as medical applications, games, advertisement, education applications, and military training. With the development of high resolution televisions, stereo televisions for providing a stereoscopic image are expected to be widely used in the future.
Related art stereoscopic displays are divided into displays using glasses (e.g., viewing glasses worn by a user) and glassless displays. In general, as shown in FIG. 1A, a related art stereoscopic display using glasses includes a liquid crystal display (LCD) 100 displaying an image with a predetermined polarization component, a micro polarizing screen 110 changing the polarization direction according to an image for a left eye and an image for a right eye of the LCD 100, and polarization glasses 120 transmitting images with different polarization states for the left eye and the right eye. For example, the micro polarizing screen 110 is a combination of 0° retarders 110a and 90° retarders 110b that are alternately interspersed. Also, the polarization glasses 120 include a pair of polarization plates 120a and 120b, through which light with different polarization states are transmitted. Since the micro polarizing screen 110 makes the polarization directions of the left-eye image and the right-eye image different from each other, and the polarization glasses 120 separately transmit the left-eye image and the right-eye image, a viewer wearing the polarization glasses 120 can see a 3D image.
However, the related art stereoscopic display has a disadvantage in that the viewer must wear the polarization glasses 120 to see a 3D image. In response, a glassless related art stereoscopic display has been developed. The glassless stereoscopic display obtains a 3D image by separating an image for a left eye from an image for a right eye. In general, related art glassless stereoscopic displays are divided into parallax barrier displays and lenticular displays. In the related art parallax barrier display, images to be seen by the left and right eyes are displayed in an alternate vertical pattern, and the pattern is seen using a very thin vertical lattice (i.e., a barrier). By doing so, a vertical pattern image to be seen by the left eye and a vertical pattern image to be seen by the right eye are separated by the barrier. As a result, the left and right eyes see images from different viewpoints so as to see a 3D image.
According to the parallax barrier display, as shown in FIG. 1B, a parallax barrier 50 including apertures 55 and masks 57 formed in a vertical grating pattern is disposed in front of an LCD panel 53 that has left-eye image information L and right-eye image information R respectively corresponding to a viewer's left eye LE and right eye RE. Each eye sees a different image through the apertures 55 of the parallax barrier 50. The left-eye image information L to be input to the left eye and the right-eye image information R to be input to the right eye are alternately formed in a horizontal direction in the LCD panel 53. If the parallax barrier 50 is disposed in a horizontal direction as well as a vertical direction, both the horizontal parallax and vertical parallax can be created, thereby providing a better stereoscopic image.
Meanwhile, to provide either a 2D image or a 3D image according to an image signal displayed on a display device, the related art glassless stereoscopic display is required to switch between a 2D mode and a 3D mode. To this end, a variety of switchable related art stereoscopic displays have been developed. For example, according to the stereoscopic display disclosed in U.S. Patent Application Publication No. 2004-0109115, two micro retarders including a plurality of vertical stripes are relatively moved to provide a 2D image or a 3D image. However, the stereoscopic display disclosed in U.S. Patent Publication No. 2004-0109115 provides a 3D image using only horizontal parallax, resulting in a limitation to obtain a better 3D image.